This research will be concerned with selected aspects of microbial iron metabolism, namely, the interaction of the high affinity iron transport compounds (siderochromes) with cell surface receptors. The binding of specific siderochromes such as ferrichrome and ferric enterobactin to outer membrane components, which also function as common receptors for certain bacteriophages and colicins, will also be studied. The biological activity of the optical and geometrical coordination isomers of hydroxamate type siderochromes, and the regulation of the high affinity iron transport system, will be investigated in enteric bacteria.